In modern telecommunication networks there is a requirement to deliver high data rate over a wide area. A proper method to increase data rate is to increase the signal levels and thus increase the signal to noise ratio (SNR). As the output power of sending stations normally is limited, the received power reduces over a wide area. Relay stations are provided in some networks for this reason. These relay stations receive the data sent by the sending station and re-send the data with a signal level higher than the level of the received signals.
In addition, more sophisticated methods to improve the data transmission exist in modern networks, such as antenna diversity and multiplexing, which uses multiple antennas for the sender and/or the receiver. This technology is also referred to as “Multiple Input Multiple Output”, MIMO for short. MIMO technology enhance link throughput by spatially multiplexing the data streams and has attracted attention in wireless communications, since it offers significant increases in data throughput without additional bandwidth or transmit power. This is achieved by higher spectral efficiency (more bits per second per hertz of bandwidth) and link reliability or diversity (reduced fading).
In the original form such techniques were proposed for point to point links providing multiplexing gains to increase the loadable throughput. However, recently these techniques have been proposed to address the problem of interference mitigation in MIMO downlinks for systems such as LTE (Long Term Evolution) and WiMAX (Worldwide Interoperability for Microwave Access). This development extends the MIMO techniques to point-multipoint systems, also termed cooperative MIMO.
One example for the MIMO data transmission is disclosed in EP1392004, which is related to a method of transmitting data signals from at least one transmitting terminal with a spatial multiplexing means to at least two receiving user terminals, each provided with spatial diversity receiving means.
Furthermore, US 2006/0164972 discloses a scheduler for scheduling downlink transmissions of orthogonal frequency division multiple access (OFDMA) signals using spatially directed beams to a plurality of subscriber stations in a wireless network. The scheduler then schedules the downlink transmissions as a function of frequency, time, and space. The scheduler further schedules downlink transmissions to a first subscriber station based on a first null space associated with at least one subscriber station previously scheduled to receive.
However, in spite of all efforts which have been made for radio networks so far, there is still room for improvement. Accordingly, the objective of the invention is to provide a method and a radio network which provide for data transmission with cooperating transmitter stations and relay stations for range extension.